Air filter



FIG. 1 is a top perspective view of the claimed design;

FIG. 2 is a bottom perspective view of the claimed design of FIG. 1;

FIG. 3 is a top view of the claimed design of FIG. 1;

FIG. 4 is a bottom view of the claimed design of FIG. 1;

FIG. 5 is a front view of the claimed design of FIG. 1, the rear view being a mirror image of FIG. 5; and,

FIG. 6 is a left side view of the claimed design of FIG. 1, the right side view being a mirror image of FIG. 6.

Any broken lines in the drawings and unshaded surfaces between the broken lines illustrate portions of the air filter that form no part of the claimed design. 

CLAIM I claim the ornamental design for an air filter, as shown and described. 